1. Field of the Invention
The present invention relates to a plasma display panel and a method for driving the same.
2. Description of the Related Art
A plasma display panel (PDP) is a type of display device that has a plurality of discharge tubes arranged in a matrix form, and it selectively makes them radiate to reconstitute picture data input as electrical signals. The driving method of the PDP is classified into a DC (direct current) driving method and an AC (alternating current) driving method, according to whether or not the polarity of the voltage applied to sustain a discharge is changed with an elapse of time.
The general PDP is a display device in which an ultraviolet ray emitted from a discharge of each pixel cell excites a fluorescent material coated on the inner wall of the pixel cell to realize a desired color. To achieve color display, the PDP must exhibit an intermediate gradation. The method for exhibiting an intermediate gradation that is currently used involves dividing one TV field into a plurality of sub-fields and subjecting the sub-fields to time division control.
There are two methods for exhibiting an intermediate gradation: an ADS (Address Display Separated) driving method and an AWD (Address While Display) driving method.
As an example in the ADS driving method, in order to display a 256-gradation image, one frame is time-divided into eight sub-fields, each of which is subject to time division into a reset period to initialize a screen, an address period to sequentially scan the screen and write data, and a sustain discharge period to sustain the luminescent status of each data-written discharge cell for a predetermined period of time, thereby driving the PDP. Here, the address period is allocated equally to each sub-field, but the sustain discharge period is allocated to the respective sub-fields at a rate of 2n (0, 1, 2, . . . , 7). Then the respective sub-fields realize a gradation in proportion to the sustain discharge period, and the gradations of the respective sub-fields are combined into a gradation for an image of one frame.
The ADS driving method is problematic in that the brightness is too low, because the sustain discharge period is shorter than the address period. In addition, the sustain discharge must be activated again after addressing the whole screen, so that wall charges generated in the discharge cells are heterogeneous due to the elapsed time for the address period, thereby causing a false discharge and a heterogeneous discharge during the sustain discharge period and hence a deterioration of the image quality.
Unlike the ADS driving method, the AWD driving method does not involve time division into a reset period, an address period, and a sustain discharge period. In the AWD driving method, a sustain discharge pulse of a predetermined frequency is successively applied to scan and sustain electrodes, and addressing is partly performed every period of the sustain discharge pulse. So the sustain discharge occurs over one frame without a discontinuance. Advantageously, the AWD driving method enhances the brightness because the sustain discharge period is sufficiently long.
In both the ADS driving method and the AWD driving method, however, the individual sub-fields consist of a reset period, an address period, and a sustain discharge period, and a large amount of ineffective light is generated due to reset and erase pulses in the reset period, resulting in a deterioration of contrast.